China has deployed 10 satellites to help in the massive air-and-sea search for the Malaysia Airlines plane missing with 239 people on board.

About two-thirds of the 227 passengers and 12 crew, now presumed to have died aboard the plane, were Chinese.

China has urged Malaysia to speed up efforts to find the aircraft and if the loss is confirmed it will be China's second-worst air disaster.

The high-resolution satellites, which are controlled from the Xian Satellite Control Centre in northern China, will be used for navigation, weather monitoring, communications and other aspects of the search-and-rescue.

Crews from nine countries have joined the international search effort, including China, Malaysia, Australia, the United States, Singapore, Vietnam, New Zealand, Indonesia, and Thailand.

Experts remain mystified as to what caused the plane to suddenly disappear from radar.

Neither Malaysia's Special Branch - the agency leading the investigation locally - nor spy agencies in the United States and Europe have ruled out the possibility that militants may have been involved in downing the flight.

But Malaysian authorities have indicated the evidence so far does not strongly back an attack as a cause for the aircraft's disappearance, and that mechanical or pilot problems could have led to the apparent crash, US sources say.

"There is no evidence to suggest an act of terror," said a European security source, who added that there was also "no explanation what's happened to it or where it is."

Thai police say two men who used stolen passports to board the missing plane were more likely to be asylum seekers, than terrorists.

Interpol has confirmed the pair had used passports which were stolen in Thailand in the past two years, leading to speculation the plane had been attacked.

But Thai investigators say an Iranian man bought the plane tickets for the men through a travel agent in Thailand.

The head of Malaysia's Civil Aviation Authority, Azharuddin Abdul Rahman, says CCTV footage of the men has been examined closely.

"And as the features of those two passengers, we have looked, have looked and relooked at the footage of the video and the photograph ... it is confirmed that they are not Asian-looking men," he said.

Spy satellites find no evidence of explosion

Also raising doubts about the possibility of an attack is that the United States extensively reviewed imagery taken by spy satellites for evidence of a mid-air explosion, but saw none, a US government source said.

The source described US satellite coverage of the region as thorough.

Interpol says it is checking whether others on board the flight had been using false identity documents.

Electronic evidence indicates the flight may have turned back towards the Malaysian capital of Kuala Lumpur before disappearing.

Even that information has not been clearly confirmed as the aircraft had failed to make automatic contact with a flight data-monitoring system after vanishing from radar screens, two people familiar with the matter said on Monday.

Such contact could have helped investigators determine what happened.

The aircraft was equipped with a maintenance computer capable of talking to the ground automatically through short messages known as ACARS.

"There were no signals from ACARS from the time the aircraft disappeared," a source involved in the investigations said.

Burrows family waiting in hope but braced for the worst

While authorities scour the area, families are still waiting anxiously for news of their loved ones.

The family of missing Australians Rod and Mary Burrows released a statement saying they are "waiting and hoping for the best".

The search area now has a radius of 100 nautical miles from the point where the plane was last detected.

Itnow takes in a larger portion of the Gulf of Thailand between Malaysia and Vietnam and land along the Malay Peninsula.

"We'd like to thank everyone for their thoughts and prayers and ask that they continue," the family said.

"Our family is still trying to come to terms with this terrible tragedy and anxiously awaiting any news or updates regarding the disappearance of flight MH370.

"The enrichment and strength that Rod and Mary have given us helps us to get through each moment during this very difficult time. It is comforting to know that Rod and Mary are together, wherever they are."

The family say they have gathered together and while they try to maintain hope, they are bracing each other "for the worst".

"We are grateful to all the organisations and countries providing the extensive search and rescue operations and our prayers and thoughts include the families of the other passengers and crew on board the flight," the statement said.

A total of six Australians were on the flight, with Springfield Lakes couple Robert and Catherine Lawton and Sydney couple Gu Naijun and Li Yuan also missing.